Biological Organization at the Cellular and Supercellular Level: A Symposium Held at Varenna, 24-27 September, 1962, under the Auspices of UNESCO

THE ROLE OF THE NUCLEIC ACIDS
IN THE PROCESSES OF INDUCTION,
REGULATION AND DIFFERENTIATION
IN THE AMPHIBIAN EMBRYO AND THE
UNICELLULAR ALGA, ACETABULARIA
MEDITERRANEA

J. BRACHET

Université libre de Bruxelles, Bruxelles, Belgium

SUMMARY

The role of nucleic acids (DNA and RNA) during cleavage and differentiation
in amphibian eggs is discussed, with special emphasis on the mechanisms of DNA
synthesis in normal embryos and lethal hybrids, and on the RNA distribution
during development.

The importance of the cell nucleus for RNA and protein synthesis in the
unicellular alga Acetabularia mediterranea is discussed on the basis of recent
experiments: it is suggested that ribosomal RNA lies under a much closer nuclear
control than transfer and chloroplastic RNA's.

A hypothesis concerning the role of messenger and ribosomal RNA in morphogenesis is presented.

INTRODUCTION

In the following, a summary is presented of current knowledge about
DNA, RNA and protein interactions during morphogenesis. Two biological systems, amphibian eggs and the unicellular alga Acetabularia,
both of which have been extensively studied in our laboratory, win be
discussed from that viewpoint. The present report will end with an
attempt to integrate the biological and biochemical observations made
on these two morphogenetic systems in a more general hypothesis of
differentiation, at the molecular level.

EXPERIMENTAL EVIDENCE

A. Amphibian eggs development

1. DNA synthesis during development

Multiplication of the cell nuclei, during cleavage, is an obvious
requirement for the morphogenetic movements characteristic of gastrulation and neurulation: only relatively small cells have the plasticity
required for this phase of development.

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